This invention relates to an improved circuit for separating the synchronizing pulses from a black and white or color composite video signal and, more particularly, to an improved sync separator circuit wherein the addition of a semiconductor element enables the slicing level of the sync separator circuit to be varied in accordance with the level of the automatic gain control (AGC) signal.
The image seen by a television camera and which is broadcast to a remote TV receiver is synchronized by horizontal and vertical synchronizing pulses which are included in the composite video/sound signal in a well known manner. The typical TV receiver first separates the sound from the received signal and then separates the synchronizing pulses from the video information. Since the maximum amplitude of the sync pulses is greater than the maximum amplitude of the video information, this separation is achieved by a switch, or sync separator, that is biased to a slicing level located between the maximum values of the sync pulses and video information. Video information and sync pulse voltage levels below the slicing level cause the switch to be open and therefore are not passed therethrough whereas sync pulse voltage levels above the slicing level cause the switch to be closed and are passed therethrough. As the characteristics of the composite signal received by the TV receiver varies, it is also desirable to vary the slicing level of the sync separator.
Accordingly, one object of this invention is to provide an improved sync separator circuit to provide a variable slicing level.
Another object of this invention is to provide an improved sync separator circuit having a variable slicing level by adding thereto at least one semiconductor device.
Still another object of this invention is to provide an improved sync separator circuit in which the automatic gain control (AGC) signal is used to vary the conduction of a semiconductor element to thereby vary the slicing level.